Electronic equipment, such as computers and communication devices often use a processor that is mounted in a socket. The socket is, in turn, mounted on a motherboard, such as a printed circuit board that connects the processor to other components. Several other devices on the motherboard may also use a socket, depending on the particular design. The socket allows the processor to be installed safely on the motherboard and allows the processor to be replaced with a faster or different model or as a repair. In a typical connection, the processor has a large number of pins or contact pads that electrically connect to a corresponding set of interconnects in the form of pins or contact pads on the socket. Often the interconnects on the socket are spring loaded or designed to have some resilience. The springiness allows all of the interconnects to make a clean connection even if the processor pins are not all perfectly aligned or if the processor's package is not perfectly flat.
The high speed of the data that is routed through many of the interconnects on the socket require interconnects that have very clean electrical properties. With higher speed data, the electrical requirements include impedance matching, low insertion loss and low cross-talk. These and other electrical effects can interfere with the data, making it unusable by the processor or by a device with which the processor is trying to communicate. However, in recent years, signal speed through the socket interconnect has doubled almost every two years. The speed increases place increasingly difficult requirements on the interconnects. With higher frequency data signals, the package and socket vertical interconnect may limit the speed at which data can be communicated.
Two reasons that vertical interconnects degrade the I/O (input/output) performance of a computer system are impedance mismatch between the processor and the socket and cross-talk between the socket pins. The cross-talk can be generated by inductive coupling between pins and capacitive coupling between pins. Inductive coupling is caused by the mutual inductance between two adjacent conductors, in this case the interconnects or pins. Capacitive coupling is due to the mutual capacitance between the two conductors.
While the mutual inductance and mutual capacitance between pins is not frequency dependent, the cross talk caused by the mutual capacitance and mutual inductance can be reduced by reducing the frequency of the signals. However, reducing the data signal frequency slows the data rates that the processor can support. They can also be reduced by moving the connectors farther apart, but many processors already use all of the available space for connectors. They can also be reduced by reducing the height of the socket pins, but this causes mechanical problems that limit the connections.